Conventionally, a surface-coated cutting tool comprising a monolayer or multilayer coating layer on the surface of a substrate of a cemented carbide, a cermet, a ceramic, or the like has been known as a cutting tool to be used widely in cutting processing of metals, printed circuit boards, etc. As the coating layer, those composed by layering a titanium carbide (TiC) layer, a titanium nitride (TiN) layer, a titanium carbonitride (TiCN) layer, an aluminum oxide (Al2O3) layer, and so on have been often used.
Having a good oxidation resistance, the Al2O3 layer among these coating layers exhibits high abrasion resistance and high capability in the processing condition in which the temperature of a cutting edge tends to be high temperature at the time of cutting, e.g., even in processing condition for processing of materials such as cast iron and alloyed steel which are hard to be cut or for high speed cutting. Especially, an Al2O3 layer made of Al2O3 with α-type crystal structure (hereinafter, referred to as α-type Al2O3 layer for short) has been conventionally used in a wide range since it has high hardness and high oxidation resistance.
For example, Patent Document 1 discloses a surface-coated cutting tool having an Al2O3 layer of Al2O3 having orientation with values of I(030)/I(104) and I(012)/I(030) greater than 1, respectively, where the peak intensity of a (hkl) plane of Al2O3 of mainly α-type crystal by x-ray diffraction analysis is defined as I(hkl) and describes that the fracture resistance of the Al2O3 layer can be improved.
Further, Patent Document 2 discloses a coated article with an texture coefficient of the (012) plane of α-type Al2O3 layer (TC: the index expressing the maximum peak intensity of diffraction peaks attributed to the (012) plane among the entire diffraction peaks of the α-type Al2O3 crystal) higher than 1.3 and describes that the particles of the Al2O3 layer can be made fine and the hardness and strength of the Al2O3 layer can be improved.
On the other hand, Patent Document 3 discloses a coated tool having an Al2O3 layer of Al2O3 with κ-type crystal structure and the surface separation of 1.43 Å (namely, diffraction angle 2θ is 65.18°) of the highest intense peak with the highest x-ray diffraction intensity and describes that the adhesion of the Al2O3 layer can be improved.    Patent Document 1: Japanese Patent Laid Open Publication No. H07-108405    Patent Document 2: Japanese Patent Laid Open Publication No. H06-316758    Patent Document 3: Japanese Patent Laid Open Publication No. H11-77407